Summary: Four different palladium and platinum bismuthotellurides, one containing major mercury, have been identified in the ore from Rustenburg mine on the Merensky Reef. The composition of each phase was determined by electronprobe microanalysis, and X-ray powder data are presented for three of these phases. Quantitative spectral reflectivity values at 470, 546, 589, and 650 mμ were obtained on areas of 1–10µ. Similar phases have been located in the ore from Union mine.

Two of these phases are shown to be moncheïte and kotulskite. From two electronprobe microanalyses, kotulskite is shown to be Pd(Te,Bi). The other two phases are new minerals: analysis of one of them gives the composition (Pd,Pt)(Te, Bi)₂, containing 23·1% Pd, 1·8% Pt, 50·8 % Te, 14·2 % Bi, with strongest X-ray powder lines at 2·92 (10), 2·10 (6), 2·02 (3), and 1·54Å (3), and cell parameters a 3·978±0·001, c 5·125±0·002; it is probably isostructural with moncheïte, and an isomorphous series may exist between them; the name merenskyite is proposed for this mineral, after Dr. Hans Merensky who was mainly responsible for discovering the platinoid bearing ‘reef’; it is commonly intergrown with kotulskite. For the second new phase (Mineral A), no X-ray data could be obtained, but a single electron-probe microanalysis gave a composition of Pd 27·8 %, Hg 12 %, Te 38·5 % and Bi 1·6 % suggesting the empirical formula (Pd,Hg)(Te,Bi).